Modern integrated circuits are customarily fabricated on substantially round slices of a semiconductor or other material, commonly called substrates or wafers. As the term is used herein, “integrated circuit” includes devices such as those formed on monolithic semiconducting substrates, such as those formed of group IV materials like silicon or germanium, or group III-V compounds like gallium arsenide, or mixtures of such materials. The term includes all types of devices formed, such as memory and logic, and all designs of such devices, such as MOS and bipolar. The term also comprehends applications such as flat panel displays, solar cells, and charge coupled devices.
In many instances during the fabrication process it is desired to place the substrate within a piece of processing equipment or a piece of inspection equipment (jointly and severally referred to as “tools” herein) in a desired position. As the term is used herein, “position” refers to two components. The first component is offset, or in other words the x,y,z location of the substrate within the plane defined by the substrate. The second component is orientation, or in other words the disposition of the substrate with respect to rotation within the plane, or the pitch and yaw of the plane as determined by a reference. It is understood that the term “position” could also refer to other components of location of an object within a three-dimensional space, but the two components described above are of primary importance in the discussion presented herein.
Currently, a variety of methods are used to place a substrate in a desire position. Formerly, the substrate would be placed on a rotating chuck and the edge of the substrate would be rotated against a physical element, such as a pin, that senses a notch or flat in the circumferential edge of the substrate as it rotates past the physical element. The substrate is then placed in a position with respect to the notch. More recently, the substrate is rotated at a relatively high rate of speed with the circumferential edge of the substrate disposed under a linear CCD element that finds the notch. The rotation again a physical element or the high rate of rotation requires that the substrate be retained to the chuck, such as by being gripped at the edge or by a vacuum chuck, but not by gravity alone.
Unfortunately, adding such pre-aligner systems to all the tools that might benefit from their use can be quite expensive, in a variety of different ways. Current pre-aligner systems have a relatively high cost of more than about six thousand dollars each, are prone to failure, and take up valuable space. What is needed, therefore, is a system that overcomes problems such as those described above, at least in part.